test: avoid false maybe-uninitialized warning

test: avoid false maybe-uninitialized warning

2026-05-29T16:05:02.6627742Z In file included from ../src/basic/../fundamental/assert-util.h:8,
2026-05-29T16:05:02.6628349Z                  from ../src/basic/assert-util.h:4,
2026-05-29T16:05:02.6628722Z                  from ../src/basic/basic-forward.h:17,
2026-05-29T16:05:02.6629044Z                  from ../src/libsystemd/sd-common/sd-forward.h:6,
2026-05-29T16:05:02.6629361Z                  from ../src/shared/shared-forward.h:6,
2026-05-29T16:05:02.6629648Z                  from ../src/shared/crypto-util.h:4,
2026-05-29T16:05:02.6631153Z                  from ../src/test/test-crypto-util.c:3:
2026-05-29T16:05:02.6634148Z ../src/test/test-crypto-util.c: In function ‘test_digest_size’:
2026-05-29T16:05:02.6634986Z ../src/basic/../fundamental/macro.h:95:41: error: ‘size’ is used uninitialized [-Werror=uninitialized]
2026-05-29T16:05:02.6635470Z    95 | #define _unlikely_(x) (__builtin_expect(!!(x), 0))
2026-05-29T16:05:02.6635764Z       |                                         ^~~~~
2026-05-29T16:05:02.6636287Z ../src/basic/../fundamental/assert-util.h:59:21: note: in expansion of macro ‘_unlikely_’
2026-05-29T16:05:02.6636963Z    59 |                 if (_unlikely_(!(expr)))                                \
2026-05-29T16:05:02.6637344Z       |                     ^~~~~~~~~~
2026-05-29T16:05:02.6637864Z ../src/basic/../fundamental/assert-util.h:65:25: note: in expansion of macro ‘assert_message_se’
2026-05-29T16:05:02.6638339Z    65 | #define assert_se(expr) assert_message_se(expr, #expr)
2026-05-29T16:05:02.6638642Z       |                         ^~~~~~~~~~~~~~~~~
2026-05-29T16:05:02.6639066Z ../src/test/test-crypto-util.c:136:17: note: in expansion of macro ‘assert_se’
2026-05-29T16:05:02.6639450Z   136 |                 assert_se(size == t->size);
2026-05-29T16:05:02.6639704Z       |                 ^~~~~~~~~
2026-05-29T16:05:02.6640063Z ../src/test/test-crypto-util.c:132:16: note: ‘size’ declared here
2026-05-29T16:05:02.6640590Z   132 |         size_t size;
2026-05-29T16:05:02.6640794Z       |                ^~~~